Refrigeration system with clearance seals

Abstract

In a split Stirling refrigerator, the dynamic seals about the displacer are virtually dragless clearance seals. The displacer is driven by pressure differential between a working gas and a gas in a spring volume, but the displacer movement is retarded until about peak pressure by forces resulting from fluid friction of gas flowing through the regenerative matrix. The fluid friction results in pressure differentials across the displacer, and the retarding effects of those pressure differentials can be increased to eliminate the need for any Coulomb friction to retard the displacer movement.

I claim: 
     
       1. In a refrigerator having means for generating a pressure wave in a working volume of gas, a displacer which reciprocates in a housing to displace gas in the working volume of gas through a regenerator and a spring volume of gas of relatively stable pressure in contact with an end surface of a drive piston on the displacer and separated from the working volume of gas by a fluid seal surrounding the drive piston, the displacer being driven solely by pressure differentials between the working volume and the spring volume, there being at least one retarding force applied to the displacer to retard movement of the displacer, the improvement wherein: all fluid seals between the displacer and housing are virtually dragless seals, the only significant retarding force is that resulting from fluid friction between the regenerator and the gas in the working volume, and the displacer and drive piston are sized relative to system pressures at each end of the displacer and drive piston such that displacer movement begins at about peak maximum and minimum pressures of the working volume at the warm end of the displacer and movement ends at full stroke within about 90° of the working volume pressure wave.   
     
     
       2. A refrigerator as claimed in claim 1 wherein each fluid seal between the displacer and housing is a clearance seal in which a clearance seal element comprises ceramic. 
     
     
       3. A refrigerator as claimed in claim 2 wherein said clearance seal element comprises cermet having a surface hardness of at least 60 on the Rockwell C scale. 
     
     
       4. A refrigerator as claimed in claim 1 wherein the clearance seal comprises a ceramic clearance seal element and a cermet clearance seal element, each clearance element having a surface hardness of at least 60 on the Rockwell C scale. 
     
     
       5. In a refrigerator having means for generating a pressure wave in a working volume of gas, a displacer which reciprocates in a housing to displace gas in the working volume of gas through a regenerator, and a spring volume of gas of relatively stable pressure in contact with an end surface of a drive piston on the displacer and separated from the working volume of gas by a fluid seal surrounding the drive piston, the displacer being driven solely by pressure differentials between the working volume and the spring volume, there being at least one retarding force applied to the displacer to retard movement of the displacer, the improvement that: all seals between the displacer and drive piston and the housing are clearance seals and a retarding force resulting from fluid friction between the regenerator and the gas in the working volume, including a pressure differential across the displacer, is at least 99% of the retarding force applied to the displacer.   
     
     
       6. A refrigerator as claimed in claim 5 wherein each fluid seal between the displacer and housing is a clearance seal in which a clearance seal element comprises ceramic. 
     
     
       7. A refrigerator as claimed in claim 6 wherein said clearance seal element comprises cermet having a surface hardness of at least 60 on the Rockwell C scale. 
     
     
       8. A refrigerator as claimed in claim 5 wherein the clearance seal comprises a ceramic clearance seal element and a cermet clearance seal element, each clearance element having a surface hardness of at least 60 on the Rockwell C scale. 
     
     
       9. In a refrigerator having a compressor for generating a pressure wave in a working volume of gas, a displacer which reciprocates in a housing to displace gas in the working volume of gas through a regenerator in the displacer, and a spring volume of gas of relatively stable pressure in contact with an end surface of a drive piston on the displacer and separated from the working volume of gas by a fluid seal surrounding the drive piston, the displacer being driven solely by pressure differentials between the working volume and the spring volume, there being at least one retarding force applied to the displacer to retard movement of the displacer, the improvement of: each fluid seal between the displacer and drive piston and the housing being a virtually dragless clearance seal in which a clearance seal element comprises ceramic and the retarding force to the displacer resulting from fluid friction is the primary retarding force on the displacer, all other retarding forces being virtually zero; and   the peak working volume pressure P pw  at the warm end of the regenerator, the cross-sectional area A C  of the displacer in the working volume, the spring volume pressure P s , the cross-sectional area A s  of the drive piston and the fluid flow characteristics of the gas through the regenerator resulting in a pressure differential at P pw  are such that (P pw  -P s ) is about equal to δ(A c  /A s ) and displacer movement begins at about maximum and minimum peak pressures P pw .   
     
     
       10. A refrigerator as claimed in claim 9 wherein said clearance seal element comprises cermet having a surface hardness of at least 60 on the Rockwell C scale. 
     
     
       11. A refrigerator as claimed in claim 9 wherein the clearance seal comprises a ceramic clearance seal element and a cermet clearance seal element, each clearance element having a surface hardness of at least 60 on the Rockwell C scale.